Magnesium hydride explosive compositions



3,053,710 Patented Sept. 11, 1962 3,053,710 MAGNESIUM HYDRIDE EXPLOSIVE COMPOSHIONS Oliver Osborn and Charles William McCutchen, Lake Jackson, Tern, and Joseph R. Hradel, Mount Pleasant, Mich, assignors to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No Drawing. Filed Dec. 12, 19 57, Ser. No. 702,224 13 Claims. (Cl. 149--45) This invention relates to novel explosive compositions and is more particularly concerned with explosive compositions having a wide range of applications and prepared from readily available and relatively inexpensive inorganic materials.

It has long been desired that readily available inorganic oxidizers be used as explosives. However, because of the difliculty of detonating, ensitizing, and storing these materials under the normal conditions of use, their wide- Spread acceptance has not been previously accomplished. Generally, if they are subject to spontaneous decomposition, their burning rate is either sufficiently slow so as to give low energy efliciencies, or else so rapid as to cause incomplete reaction of all the inorganic oxidizer before it is dispersed by the reaction; additionally, when an inorganic oxidizer explodes, excess oxygen is generated, which is highly reactive. If this excess reactive oxygen could be utilized, additional force and power could be added to the explosion. However, this additional reaction must occur prior to dispersion of the components in order that the force of the second reaction might be cumulative. Still another problem in prior art conventional inorganic explosives has been the fact that certain of the combustion produtcs are toxic and, therefore, add a deleterious health factor, making them unsuitable for use in many applications. Also, with many organic explosives, such as dynamite, it is essential for safe storing that regular rotation of the organic explosive be carried out, else the sensitivity is increased substantially. In conventional dynamite handling, this is known as turn over.

It is, therefore, a principal object of the present invention to provide an explosive mixture prepared from readily available inorganic components. Still another ject of the present invention is to provide an explosive composition containing magnesium hydride and an inorganic oxidizer. A further object of the present invention is to provide explosive mixtures which, by varying the amount of magnesium hydride and selecting the particular inorganic oxidizer therein, may be utilized as a deflagrating, detonating, primary, secondary, high explosive, low explosive, or rocket propelling explosive. Still a further object is to provide an explosive which, if it deteriorates, becomes less sensitve on storage rather than more sensitive. Other objects will become apparent hereinafter.

When ammonium nit-rate explodes, the following chemical reaction occurs:

The complete detonation and control of detonation of ammonium nitrate by itself is a most difiicult problem. In some instances, depending on the temperature and pressure of the reaction chamber, complete, incomplete or failure of the explosion occurs. While purity and particle size of the ammonium nitrate are definite factors, up to the present time, it has been practically impossible to accurately predict the results of an ammonium nitrate explosion. The same problems are generally present with other inorganic oxidizers used as explosives. It will be noted in the above reaction that oxygen is formed.

This oxygen is available to combine with an additional reactant with a concomitant release of additional energy affording an enhanced total available energy. It appears, that by providing magnesium hydride as a fuel to combine with the generated oxygen resulting from the decomposition of the ammonium nitrate, various other Since all or" these reactions involve the liberation of e ergy, the total energy provided from such reactions in combination with the energy of the ammonium nitrate decomposition results in an energy potential substantially greater than that obtainable from ammonium nitrate alone. The exact reaction which predominates is not known at this time, but each reaction is presumed to be occurring at least to some extent. In the event the reaction which predominates involves the decomposition of the metallic hydride with the production of free magnesium therefrom, this free magnesium will react with the water present to prepare magnesium oxide and hydrogen. Heat is thereby generated, which also is added to the energy of the main reaction, to increase its explosive force. Similarly, additional energy is generated upon decomposition by the addition of magnesium hydride to other ionizable, decomposable, oxygen-containing, inorganic solids.

While the above reactions add to the energy of the base decomposition reaction, it has also been found that magnesium hydride serves to sensitize the decomposition of many inorganic oxidizers. Not only is the decomposition caused to occur more readily and more completely, but unexpectedly. This sensitization occurs at concentrations of magnesium hydride substantially below stoichiometric; thus, for example, with ammonium nitrate, seven percent magnesium hydride gives a mixture which substantially completely decomposes under conditions at which ammonium nitrate alone will not decompose or decomposes incompletely. Also, with sodium ni trate, which by itself is stable and does not decompose except under extreme conditions, with the addition of as little as six percent magnesium hydride, sodium nitrate will decompose with a No. 10 electric blasting cap.

Inorganic materials which are suitable must fit the following qualification: When these materials are stoichiometrically balanced in a reaction with MgH a summation of the free energies of formation of the products must be more negative than the summation of the free energies of the reactants.

To determine the suitability of various inorganic materials with respect to thermodynamics for application to the compositions of the present invention, it is necessary to theoretically calculate the free energy of both sides of the proposed reaction. A simple method of determining the suitability is to calculate the total free energy of formation on each side of the reaction. Then, if the free energy of formation of the reaction products is more negative than the total free energy of formation of the reactants, the reactant is suitable for use in the composition of the present invention. The free energy of formation values for most materials are readily available in most sources listing physical data of chemical compounds, or may be determined experimentally by conventional methods. For these purposes, magnesium hydride may be said to have a free energy of formation of 8.5 kcal. per gram mole. To illustrate the technique for calculation, an example may be made of NH NO It is assumed to react in the following manner:

It will be noted that two moles of NH NO react with one mole of MgH to produce one mole of MgO, two moles of N and five moles of water. To calculate the free energy of formation on each side of the equation, we find the free energy of formation of NH NO is --76, multiplied by 2 is 152 and added to 8.5, gives 160.5. The NH NO free energy of formation is multiplied by 2 because two moles of ammonium nitrate enter into the reaction. Thus, thermodynamically, the left hand side of the equation may be said to have a value of 160.5. Repeating the same procedure for the right hand side of the equation, magnesium oxide has a free energy of formation of 136, added to (an element, N by definition has a free energy of formation of 0), added to 5 57 (5 moles of water result in the reaction) gives a value of (285)+(136)+0=-421. Thus, the right hand side of the equation is more negative than the left hand side of the equation, and NH NO would be thermodynamically suitable for the composition of the present invention. Other examples of thermodynamic calculations which show the calculations are:

This material is suitable since 89.7 is more negative than 48.1.

All of the above equations are more negative on the right hand side than on the left hand side of the equation, indicating their thermodynamic suitability for the compositions of the present invention.

Other thermodynamic equations which can be exemplified include:

None of the above materials are suitable for the compositions of the present invention because the left hand side of the equation is less than the right hand side of the equation.

Strictly speaking, the free energy of formation at the working temperature of the reaction should be used in making the above calculations. However, for practical purposes, values for free energies of formation at room. temperature may generally be employed.

In addition to showing the suitability of the various compounds for the composition of the present invention, the calculations as shown above will also indicate the potential energy available. Thus, a small proportional difference between the totals of the two sides of the equation indicates relatively little potential energy available, while a relatively large proportional difference indicates relatively large amounts of potential energy available from the reaction. However, these calculations do not indicate the speed of the reaction which will affect the available energy for various applications.

Representative oxidizers which may be considered are: ammonium nitrate, sodium nitrate, potassium nitrate and other stable nitrates, sodium, potassium and lithium chlorates, sodium, potassium and lithium perchlorates, sodium, potassium and lithium permanganate, sodium, potassium and lithium persulfate, strontium nitrate, aluminum nitrate, lead nitrate, mercuric nitrate, calcium nitrate, magnesium nitrate, nickel nitrate, magnesium perchlorate, beryllium nitrate, cupric bromide, cobalt sulfide, ferrous sulfide, mercuric bromide, molybdenum carbide, mercuric sulfide, mercuric iodide, lead sulfide, lead fluoride, lead chloride, ferric nitride, bismuth sulfide, arsenic sulfide, etc. The inorganic solid is mixed with varying quantities of magnesium hydride by any convenient safe method. Because the materials of the present invention are explosive, care and adequate safeguards are in order for handling, mixing, storing and using the materials.

The particulation of both the oxidizer and the magnesium hydride has considerable effect on the sensitivity of the resulting explosive composition. For example, on the detonation of a loosely-mixed, relatively large particle sized ammonium nitrate, it will be noted that the detonation intensity is less than with substantially smaller particle sizes under the same conditions. Similarly, coarser grains of magnesium hydride achieve a lower sensitivity than do finer particle sizes.

While the amount of magnesium hydride employed may be varied over a rather wide range, various percentages as employed will aifect the properties of the final mixture. For example, the amount of initiation required will be inversely affected by the amount of magnesium hydride present, if the same particle sizes are employed. Thus, with approximately 4 percent magnesium hydride present at a particle size of about 28 mesh intimately mixed with ammonium nitrate, a No. 6 electric blasting cap will initiate a detonation, while with one percent of the same magnesium hydride present with ammonium nitrate, a No. 10 electric blasting cap is required. Generally, a maximum sensitivity point can be reached after which the mixing of additional or finer particle sized hydride does not increase the sensitivity. Sensitivity point is somewhat below the stoichiometric quantity of MgH While the conventional safeguards usually employed in the mixing, handling, and using of the explosives of the compositions of the present invention should be employed at all times, preliminary studies indicate that the compositions of the present inventionare at least as safe as conventional explosives. They appear to store well with or without the exclusion of moisture, although longer storage periods are possible in a moisture-excluding container. In any event, in direct contrast to dynamite, which becomes more sensitive with age, the compositions of the present invention become somewhat less sensitive with age. This then constitutes an inherent safety factor.

' Squib-electric black powder ignitor Preliminary storage and stability studies have shown that storage in unsealed containers for periods as long as five months have shown no deleterious effect on the sensitivity or power of the material of the present invention.

Besides the storage and stability advantages of the compositions of the present invention as compared with conventional explosives, other distinct benefits are present. The reaction products are generally less toxic than those of many conventional explosives. The ease of handling a solid magnesium hydride as contrasted with the usual liquid sensitizers is apparent. Additionally, the solid mixture of the present invention is not subject to freezing, a problem with most conventional explosives.

While the invention has been particularly described as a two-component system, it is to be understood that a mixture of inorganic materials may be employed for special applications. Alternatively, various burning rate moderators, buffers or fillers may be added to accomplish specific purposes without departing from the present invention.

The following examples are given to illustrate the present invention, but are not to be construed as limiting the invention thereto.

Example I Except for the blank, stoichiometric quantities of magnesium hydride were mixed with the inorganic oxidizing materials listed in column 1. The magnesium hydride and oxidizer were separately ground with a mortar and pestle and thereafter mixed on a sheet of clean paper with a spatula. The formulations were loaded loose into an empty No. 6 blasting cap and compressed by pushing and crimping a time fuse into position. Six inch lengths of 45 seconds/foot time fuse in combination with the standard Engineer Corps fuse lighter were employed as initiators.

All of these materials can be ignited by conventional electrical means and indicate utility as primary explosives. A primary explosive may be defined as an explosive sensitive to a time fuse or a heated filament.

Example II (A) A series of 200 gram loads of ammonium nitrate with 7.6 and 19.3 percent magnesium hydride were placed in polyethylene bags and initiated with the listed commercial devices.

The results are tabulated below:

Initiator 7.6% MgHq 19.3% MgH Engineers special blasting cap No. 8 electric blasting cap N0. 6 electric blasting cap These tests show that detonation is possible, even though the material is unconfined. They also indicate that the initiator force for detonation is inversely proportional to the quantity of MgH present.

(B) A series of 75 gram loads of 14.2 and 24.7 percent magnesium hydride-ammonium nitrate shots were prepared by intimately mixing the components and loaded into a 1" x 6" steel nipple capped at both ends with one cap drilled to accept the leg wires of the initiator. The results are tabulated below:

Initiator 14.2% MgHz 24.7% MgH E.S.B.O Fir d Fired. No.8E.B.O Do. No.6 E.B.O-- Do. Squib DO.

14.2% mix 24.7% mix Initiator used Velocity at Duration Velocity at Duration .0001 sec., of flame, .0001 sec., of flame,

ftJsec. sec. ft./sec. sec.

The above results indicate that these magnesium hydride formulations classify as deflagrating explosives. De-flagrating, as used herein, is an explosive which, during reaction or shortly before, shows a flame.

Example 111 By repeating the procedure of Example II(B) with smaller amounts of MgH it was determined that fine fertilizer grade ammonium nitrate has a true detonation point at one percent MgH with the Engineer special blasting cap (equivalent to a commercial No. 10 electric blasting cap), while with a No. 8 electirc blasting cap fine fertilizer grade ammonium nitrate has a true detonation point with two percent MgH With a No. 6 electric blasting cap, the true detonation point is with four percent magnesium hydride, while an electric squib initiator does not show any substantial breaks in the curve. True detonation may be defined as an explosion in which no flame is visible before or during detonation. All of the above figures were obtained with a 28 mesh magnesium hydride.

Example IV Five-month compatibility studies for a mixture of 14.2 percent magnesium hydride in intimate mixture with prilled fertilizer grade ammonium nitrate, stored out-ofdoors in cardboard containers with no attempt made to exclude moisture showed no deleterious effects, either in sensitivity or in moisture content. However, extended storage should be carried out under moisture-proof conditions, as some absorption of the water was noted.

Example V A number of 2.36 inch rockets were loaded with 50- gram charges of various oxidizing agent intimately mixed with varying quantities of magnesium hydride. These rockets were launched from a 3-inch diameter, 6-foot length pipe, and fired horizontally with a time fuse employing nonelectric caps made up of NaNO -MgH mix.

The rockets were aimed at an earth embankment 50 feet from the launching sight with the following results:

1" X 6" nipples, capped at both ends, with one cap drilled to accept the blasting cap fuse train. The follow- Percent Extent of Flight Earth Oxidizer component OXlt'iZer Type of reaction Rate of reaction reaction plus penetra.,

wi dist., MgHz yd.

2.36 rocket propellant 50 1 LiNO; O 2

KNO3 starch- 50 2 NaNO: starch. 50 2%;

Mg(ClO )2 starch Extremely fast 50 3 Mg(NO )2-6HgO 62.0 Very fas 50 2 A1(NO -9H2O 61. 5 0 .d0 50 1% N 9.010 starch 55.0 o Extremely fast- 50 3 NagSzOs 50.0 Burn to detonate 50 0 NazSzOa 53. 2 Burning Fast 50 1 1 M-7 propellant-Specific Impulse 240.

The above tests show that even when a burning inhibitor is employed with certain of the explosives of the present invention, an outstanding rocket propellant composition has been provided. 'It should also be noted that excellent results were obtained on the above even in the absence of an organic fuel binder.

Example VI In order to demonstrate the utility of a variety of oxidizer agent in combination with MgH 50 grams of a mixture comprising these agents were intimately mixed with magnesium hydride and placed in a 4-ounce stoppered bottle and fired with a No. 8 electric blasting cap. The following results were obtained:

Oxidizer Oxidizer Detonation Flash Remarks percent 75. 3 Very good Bright- Fast. 85. 8 do Slight--- Do. Do. Do. Do. Medium Fast. Fairly fast. 0&(N O3)g-4HzO Medium. Mg(NO.".)2'6HzO- 62.0 0 Ni(N Oak-61120.--. 65.0 Very good Mg(Cl0i)z 51. d0

HS 54. 5 Good.

59. 3 do Nags-s 50.0 Very good--.

Example VII To demonstrate the primer characteristics of the mixtures of the present invention, various test formulations comprising oxidizing agents containing intimately mixed stoichiometric quantities of magnesium hydride by placing the formulations in No. 6 blasting cap shells, packing it as tight as possible with the end of a time fuse, and crimping. A base charge of 75 grams of a 24.7 percent magnesium hydride mixed with ammonium nitrate and other 75-gram base charges of tetryl and TNT were provided. These base charges were individually placed in ing results were obtained, HO signifying a high order explosion and LO signifying a low order explosion:

High and low order explosions, as used herein, describe the apparent velocity of detonation.

Primer composition 24.7% MgH TNT NH4NO3 Fired HO.

Failed. Fired HO.

Do. Do. Failed.

MgHz-BMNOzO 1 Flash.

Example VIII A stoichiometric mixture containing 26 parts of magnesiurn hydride and 224 parts of CuBr by weight was prepared by intimately mixing the ingredients in a. mortar and pestle. Representative samples were tested for impact detonation by hitting a plunger onto the samples supported on a steel plate. In each instance, a sharp report and flash were noted When the impact was sufliciently great.

In a manner similar to that of :the foregoing examples, other solid, neutral, inorganic materials whose energy of formation in combination with the free energy of formation of magnesium hydride when stoichiometrically balanced in a reaction is thermodynamically less negative than the total energy of formation of the reaction products of said reaction, may be substituted for those specific materials shown in the examples. Representative materials which may be substituted, include, for example, potassium chlorate, potassium perchlorate, potassium nitrate, potassium bisulfate, potassium bicarbonate, potassium borate, potassium carbonate, potassium chromate, potassium perchromate, potassium permanganate, potassium phosphate, potassium sulfate, potassium thiocyanate, aluminum chlorate, aluminum nitrate, aluminum sulfate, ammonium carbonate, ammonium chlorate, ammonium dichromate, ammonium nitrate, ammonium perchlorate,

ammonium perchromate, ammonium phosphate, ammoniunr sulfate, arsenic sulfide, barium chlorate, barium chromate, barium dichromate, barium nitrate, barium perchlorate, barium permanganate, barium persulfate, barium phosphate, barium sulfate, bismuth dichromate, cadmium chlorate, cadmium permanganate, calcium chlorate, calcium ch-romate, calcium perchlorate, calcium peroxide, potassium permanganate, chromic oxide, cobaltous perchlorate, cobaltic oxide, cupric bromide, cupric chlorate, cupric chromate, cuprous carbonate, copper sulfate, ferric oxide, ferrous perchlorate, lead oxide, lead chlorate, lead sulfate, lead perchlorate, lead persulfate, lithium chlorate, lithium chromate, lithium nitrate, lithium perchlorate, lithium permanganate, magnesium chlorate, magnesium chromate, magnesium perchlorate, magnesium nitrate, magnesium permanganate, magnesium sulfate, manganese perchlorate, manganese nitrate, mercuric chlorate, mecuric chromate, mercuric fulminate, mercuric nitrate, mercuric sulfate, mercurous chlorate, molybdenum oxychloride, nickel chlorate, nickel carbide, nickel nitrate, nickel perchlorate, nickel sulfate, rubidium chlorate, rubidium dichromate, rubidium perchlorate, silver chlorate, silver nitrate, silver perchlorate, silver peroxide, silver permanganate, sodium bisulfate, sodium borate, sodium tetraborate, sodium carbonate, sodium chlorate, sodium chromate, sodium dichromate, sodium dithionate, sodium nitrate, sodium perborate, sodium perchlorate, sodium permanganate, sodium peroxide, sodium persulfate, sodium thiosulfate, strontium chlorate, strontium nitrate, strontium perchlorate, sodium cobaltonitrate, etc.

For the purposes of this invention, the term explosive is intended to mean material which under stimulation releases substantial energy rapidly and includes primary, secondary, deflagrating, primer and propellant materials.

Various modifications may be made in the compositions of the present invention Without departing from the spirit or scope thereof and it is to be understood that we limit ourselves only as defined in the appended claims.

We claim:

1. An explosive composition comprising from 1-50 percent by weight of magnesium hydride intimately mixed with solid inorganic oxidizing materials whose free energy of formation in combination with the free energy of formation of magnesium hydride when stoichiometrically fuel-oxidizer balanced in a reaction is thermodynamically less negative than the total free energy of formation of the reaction products of said reaction.

2. An explosive composition comprising from 1-50 weight percent of magnesium hydride intimately mixed with a solid inorganic oxidizing material wherein the cation is selected from the group consisting of potassium,

sodium, lithium, ammonium, barium, lead, magnesium, aluminum, mercury, calcium, nickel and copper and wherein the anion is selected from the group consisting of chlorate, perchlorate, nitrate, persulfate, and permangamate.

3. An explosive composition comprising from 1-50 percent by weight of magnesium hydride intimately mixed with a solid inorganic nitrate.

4. An explosive composition comprising from 1-50 percent by weight of magnesium hydride intimately mixed with a solid inorganic chlorate.

5. An explosive composition comprising from l-SO weight percent of magnesium hydride intimately mixed with a solid inorganic perchlorate.

6. An explosive composition comprising from 1-50 Weight percent of magnesium hydride intimately mixed with a solid inorganic permanganate.

7. An explosive composition comprising from l-SO weight percent of magnesium hydride intimately mixed with a solid inorganic persulfate.

8. An explosive composition comprising from l-50 weight percent of magnesium hydride intimately mixed with ammonium nitrate.

9. An explosive composition comprising from 6-50 Weight percent magnesium hydride having a particle size of from 16 mesh to +325 mesh intimately mixed with ammonium nitrate.

10. An explosive composition comprising from 1-50 weight percent of magnesium hydride intimately mixed with sodium nitrate.

11. An explosive composition comprising from 1-50 weight percent of magnesium hydride intimately mixed with magnesium perchlorate.

12. An explosive composition comprising from l-50 weight percent of magnesium hydride intimately mixed with lithium chlorate.

13. An explosive composition comprising from 1-50 weight percent of magnesium hydride intimately mixed with lithium perchlorate.

References Cited in the file of this patent UNITED STATES PATENTS 2,410,801 Audrieth Nov. 12, 1946 2,477,549 Van Loenen July 26, 1949 2,573,471 Malina et a1. Oct. 30, 1951 OTHER REFERENCES Hurd: Chemistry of Hydrides, 1952, pages 51-52. Ley: Rocket Propulsion, Aircraft Engineering, September 1935, page 228. 

1. AN EXPLOSIVE COMPOSITION COMPRISING FROM 1-50 PERCENT BY WEIGHT OF MAGNESIUM HYDRIDE INTIMATELY MIXED WITH SOLID INORGANIC OXIDIZING MATERIALS WHOSE FREE ENERGY OF FORMATION IN COMBUSTION WITH THE FREE ENERGY FORMATION OF MAGNESIUM HYDRIDE WHEN STOICHIOMETRICALLY FUEL-OXIDIZER BALANCED IN A REACTION IS THERMODYNAMICAL LY LESS NEGATIVE THAN THE TOTAL FREE ENERGY OF FORMATION OF THE REACTION PRODUCTS OF SAID REACTION. 